1. Scope of the Invention
The present invention is a cannula for use in ophthalmologic operations. It is particularly useful for injecting anesthetic into the ocular region while eliminating the inherent dangers posed by using a needle to perform a similar function.
2. Description of the Prior Art
The technique for injecting anesthetic into the eye to achieve akinesia, used in approximately 90% of cataract surgeries performed, includes a series of steps. Usually, a blind passage with a sharp needle is performed through the skin below and/or above the eye into the orbital region to introduce anesthetic directly or indirectly into the retro-bulbar space. In a small, but significant, percentage of the time a second blind passage is needed because the first blind passage has not properly accessed the retro-bulbar space. Three to five cubic centimeters(ccs) of anesthetic is used. The protein hyaluronidase is used to help diffuse the anesthetic into the retro-bulbar space in case the space is missed.
It has also been proposed to follow a procedure in which a topical anesthetic is placed on the surface of the eye to minimize sensation. The topical anesthetic allows the surgeon to provide a local anesthetic to the peri-ocular region, to achieve anaesthesia. Once the topical anesthetic has taken effect, a small perforation is made with a sharp needle, piercing the conjunctiva and Tenon's capsule. The region between the Tenon's capsule and sclera, often called sub-Tenon's space, provides indirect access to the retro-bulbar space. Akinesia is achieved shortly after an anesthetic is injected and the operation then ensues.
The use of the needle to access the retro-bulbar space has proven effective. It is used in over 90% of current cataract surgeries. The use of the sharp device in the delicate ocular region, however, may have complications. Since the needle is slid around the globe of the eye, there exists the inherent risk of globe penetration. Furthermore, once the needle directly accesses the retro-bulbar region, there are the further risks of optic nerve trauma and retro-bulbar hemorrhage. Any of these injuries may lead to the complete loss of vision.
During the year immediately prior to this application, approximately 1.4 million cataract surgeries were performed. It is estimated that during the year of this application, this number will increase to approximately 1.5 million, with a continued increasing trend in the coming years. It is also estimated that approximately one out of a thousand of the persons having cataract surgery will be rendered wholly or partially blind due to the use of the needle to inject anesthetic into the retro-bulbar space.
One report of 6,000 consecutive injections indicates that one in 375 had complications of a sort that suggest a direct spread of anesthetic agent to the central nervous system through penetration by the needle of the optic nerve sheath.
Accordingly, an object of this present invention is to provide surgeons with a device which effectively administers anesthetic into the retro-bulbar region while minimizing, if not eliminating, the inherent dangers posed by the presently employed needle method.
A related object of this invention is to provide a device which is low-cost, disposable and easily adaptable to currently used medical equipment.
A further purpose of this invention is to meet the above objectives in a device which can be used with a wide variety of patients.